Copper based alloy featuring precipitation hardening and solid-solution hardening

ABSTRACT

A phosphor bronze alloy which contains 0.4 to 3.0 weight % Ni, 0.1 to 1.0 weight % Si, 0.01 to 0.35 weight % P, 1.0 to 11.0 weight % Sn with remainder being substantially Cu.

This application claims priority to U.S. application Ser. No. 60/057,777filed Sep. 5, 1997, the entire contents of which are incorporated byreference.

This invention relates to a copper alloy, particularly a copper alloythat is especially useful in electrical and electronic interconnectioncomponents and switch applications, including high temperatureswitching. This alloy shows special promise in “spring type”applications.

BACKGROUND OF THE INVENTION

Several families of copper alloys are known in various arts. Forexample, Mikawa et al., U.S. Pat. No. 5,041,176 discloses a copper alloyincluding from 0.1-10% nickel (Ni); 0.1-10% tin (Sn); 0.05-5% silicon(Si); 0.01-5% iron (Fe); and 0.0001-1% boron (B), by weight. Thisdisclosure requires formation of an Ni-Si intermetallic compoundhomogeneously dispersed in the alloy. Fe is required for age hardening.However, at Fe concentrations greater than 5%, electrical conductivityis compromised and corrosion becomes a serious problem. B isincorporated into the alloy to improve corrosion resistance, hardnessand strength. High hardness is achieved by precipitation hardening at atempering temperature of 400° to 450° C. Si also serves as a deoxidizer.

Although the Mikawa alloy is suitable for use in electronic parts wheregood electrical conductivity, heat conductivity, strength, hardness,plating ability, soldering ability, elasticity, and corrosion resistanceincluding resistance to acids are required, this alloy is of a differentcomposition and displays different characteristics from those obtainableaccording to the instant invention.

Another comparison alloy is disclosed by Kubosono et al., U.S. Pat. No.5,516,484. Kubosono et al. discloses copper-nickel based alloys that areprocessed using horizontal continuous casting with a graphite mold. TheNi—Cu alloy system is essentially a different alloy than the alloy ofthe instant invention. In this alloy copper (Cu) is an undesiredimpurity whose content must be kept below 0.02%. Kubosono et al.,teaches that effects obtainable by addition of Si cannot be recognizedif no B is present.

U.S. Pat. No. 5,334,346 to Kim et al. discloses a high performancecopper alloy for electrical and electronic parts. The Kim alloy consistsessentially of copper and 0.5 to 2.4% by weight Ni; 0.1-0.5% Si; 0.02 to0.16% P; and 0.02 to 0.2% magnesium (Mg). Kim et al. discussesprecipitation hardening where Ni₂Si and Ni₃P precipitate in the coppermatrix. Any excess of free Si and P, is taught as causing formation ofbrittle intermetallic compounds which lead to peeling and cracking. Mgis proposed as a scavenger element to remove free Si and P. However, ascontent of Mg increases, conductivity and utility of the alloy arecompromised. Zinc (Zn) and Fe are also disclosed as possible scavengers.This alloy does not contain Sn.

Hashizume et al., U.S. Pat. No. 5,064,611 discloses a process forproducing a copper alloy that contains 1-8% Ni; 0.1-0.8% P; 0.6-1.0% Si;optionally, 0.03 to 0.5% Zn; and Cu. Ni₅P₂ and Ni₂Si are disclosed asintermetallic compounds for increasing mechanical strength of the alloywith minimal decrease in electrical conductivity. Sn is not present inthis alloy.

As an example of a copper-tin alloy, i.e., bronze, Asai et al., U.S.Pat. No. 5,021,105, discloses an alloy comprising 2.0-7.0% Sn; 1.0-6.0%Ni, cobalt (Co) or chromium (Cr); 0.1-2.0% Si; and Cu. This alloy may beprocessed to exhibit elongation of 3-20%; strength of 70-100 kg/mm²; andelectroconductivity from 10-30% IACS. Ni is disclosed as being importantfor strengthening; Cr is disclosed as improving hot rolling propertiesand heat resistance; and Co is disclosed as contributing to effectiveheat resistance. According to Asai et al. Sn content is limited to 7% bythe hot rolling method used to process the alloy. Asai et al. does notdisclose phosphorus (P) as a constituent. Accordingly, this alloysuffers similar limitations to Mikawa et al., as discussed above.

Similarly, Arita et al., U.S. Pat. No. 4,337,089, discloses a Cu—Ni—Snalloy containing 0.5-3.0% Ni; 0.3-0.9% Sn; 0.01-0.2% P; 0.0-0.35%manganese (Mn) or Si; and Cu. This alloy features 60 kg/mm² tensilestrength and elongation of more than 6% (i.e., to provide the mechanicalproperty necessary for bend working) by combining heat treatment andcold rolling in its processing. In Arita et al., Si or Mn isincorporated to enhance strength. The low Sn content disclosed in Aritaet al., however, does not provide the combined formability-strengthproperties of the instant invention.

Takeda et al., U.S. Pat. No. 5,132,083 teaches a laser padding materialwhich is a powder containing 1-5% Ni; 0.2-5% Si; less than 1% ; lessthan 2% P; less than 3% Mn; and Cu. Sn and lead (Pb) are optionalingredients, at 8-15% for each. This powder can be laser processed toproduce a copper laser padding material excellent in sliding-abrasionresistance. The chemistries involved in laser padding are not the sameas in the alloy of the instant invention. For example, no rolling, hotor cold, is used to process the padding material.

A designation system for providing a means for defining and identifyingcoppers and copper alloys is known as UNS (Unified Numbering System).This system is in common use in North America and uses a five digit(recently expanded from three digit) numbering following a C prefix. Thenumbering system is not a specification, but rather a useful number codefor identifying mill and foundry products. The C designations appearingbelow refer to the UNS numbers. The general art that includes alloysthus includes many patentable alloys that are similar in some respectsin composition, but that display different desired properties dependingon the specific content and processing of the alloy.

UNS alloy C85800 is a leaded yellow brass containing 1.5% Sn, 1.5% Pb,31-41% Zn, 0.5% Fe, 0.05%Sb, 0.5% Ni (incl Co), 0.25% Mn, 0.05% As,0.05% S, 0.01% P, 0.55% Al, 0.25% Si and 57.0% minimum Cu.

In the electronics industry, phosphor bronzes with required strength andformability are known that can be used up to 100° C. However, the needexists for alloys resistant to higher temperatures, e.g., of 120° C.,140° C. and temperatures up to or exceeding 150° C. Higher temperatureapplications will allow faster speed in electronic processing and allowthe alloy to be used in higher temperature environments.

Accordingly, the present invention provides a phosphor bronze alloy withcharacteristics much improved over those known in the art. The inventionprovides an alloy that when processed has desired spring and strengthproperties and superior durability especially at higher temperatures atan economic price.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts softening behavior data curves for alloy MHP101 of theExample and of comparative alloys.

FIG. 2 depicts stress relaxation data curves for alloy MHP101 of theExample and of comparative alloys.

THE INVENTION

A particle dispersion enhanced phosphor bronze in accordance with thepresent invention includes a nickel content of from 0.4 to 3.0% byweight; a Si content of from 0.1 to 1.0% by weight; a P content of from0.01-0.35% by weight; a Sn content of 1.0-11.0% by weight and copper. Snenhances formability at a given level of strength. P helps impartoptimal spring and strength properties as well as providing fluidity incasting copper based alloys. P also aids in deoxidation of the melt. Pis the primary deoxidizer of the melt. Si is not lost in uncontrolledquantities in the melting process, which permits maintaining astoichiometrical relationship between Si and Ni in the alloy.

Sn content of below 8% and P content of 0.01-0.2% by wt. are especiallypreferred in some embodiments.

Solid solution hardening is contributed by tin, phosphorous and copper,while precipitation hardening resides in nickel silicide and nickelphosphides precipitated in the matrix.

Solid solution of a copper base occurs when the alloying element isdissolved to form a homogenous liquid solution. When the solution isfrozen and subsequently rolled/annealed, the alloying metal goes intosolution to form a solid solution. The alloying element thereby becomesan integral part of the matrix crystal.

Substitution of elements in solid solution tends to increase thestrength of the metal as it decreases electrical conductivity. Theincreased strength is related to a greater resistance to slip. Thesolute atoms are different in size from the copper atoms, causing adistortion of the lattice structure that imparts slip resistance. Thatis, greater energy is required to distort the lattice.

Preliminary analysis indicates that this alloy is resistant to stressrelaxation, i.e., time dependent decrease in stress in a solid undergiven constant constraints especially at elevated temperaturesencountered in some applications. The phosphor bronze according to theinstant invention has consistent mechanical properties, optimum yieldstrength and excellent formability. The alloy is especially useful inhigh temperature applications, e.g., where operational temperatures mayreach 140° C., 150° C. or higher, for example, up to 200° C. in specificapplications. The alloy is designed to be a high strength alloy withmoderate conductivity. In these applications, no comparable alloy hasbeen previously available.

The alloy family will have the strength and formability of knownphosphor bronzes, but will exhibit superior resistance to stressrelaxation especially at elevated temperatures.

In an exemplary process, the material for the alloy is mixed accordingto desired concentrations and melted in channel or coreless electricinduction furnaces. The obtained melt is horizontally continuous castthrough a graphite die. This process is sometimes referred to ashorizontal thin strip continuous casting. Special enhanced cooling canbe employed to assure proper quenching of solidified material, tomaintain all solute in solution.

The preferred casting practice employs special enhanced cooling withinthe graphite die assembly to assure a sufficiently rapid quench of thejust-solidified metal from its solidus temperature to a temperaturebelow 450° C. This assures that the solute remains to a high degree(estimated at approx. 90%) in solution, and does not have time tosignificantly precipitate during the cooling phase.

This enhanced cooling involves the use of high thermal conductivity(minimum 0.77 cal/cm/sec) copper plates to which a high thermalconductivity graphite die (minimum 0.29 cal/cm/sec) has been bolted asper current standard art. The invention introduces a high conductivitygas such as Helium or Hydrogen or mixtures thereof, or carrier gaseswith significant concentrations of Helium and/or Hydrogen, between thecopper plates and graphite plates of the assembly. The high conductivitygas replaces atmospheric O₂/N₂ in the copper/graphite interface, therebyimproving the cooling action.

The cast material is surface milled and then rolled down to thinnergages. Heat treatments are imposed in the course of rolling to assure 1)maximum solution of alloying elements, and 2) precipitation of thedissolved alloying elements. The precipitate provides strength andresistance to stress relaxation.

Less cold rolling is required to achieve the same tensile strength as Snconcentration (solid solution content) of the alloy increases. Less coldrolling permits more subsequent forming operations.

After heat treatment, the material is for some applications furtherrolled to attain increased strength, and may or may not be stressrelieved thermally and/or mechanically at finish.

In a further embodiment of the invention, improved solutioning of thesolute is obtained by heat treating at elevated temperatures at the caststage, or at intermediate stages.

The process stages in accordance with the instant invention can includethe following protocols:

One embodiment (for those mills so equipped)

Cast

Mill

Homogenize (=rapid heat up/homogenize/quench). The homogenizationassures maximum solutioning of alloying elements. The quench assuresmaximum solution is retained. Temperature attained is 800-950° C.

Roll

Precipitate anneal at 375-550° C. Roll to finish

Relief anneal for various tensile and yield strength conditions.

Another embodiment (for those mills so equipped)

Cast

Mill

Roll to intermediate gage

Homogenize anneal Roll

Precipitation anneal

Roll to finish

Relief anneal

Another embodiment (for maximum strength at the expense of someconductivity)

Cast

Mill

Homogenize

Roll

Rapid anneal with quench (may need multiple “anneal with quench” stepsin process to reach light gages)

Roll

Mill hardening anneal

Another embodiment

Cast

Mill

Roll to intermediate gage

Homogenize

Roll

Rapid anneal with quench (may need multiple “anneal with quench” stepsin process to reach light gages)

Roll

Alternatively, a rapid cool can replace quenching in the above-describedcasting practice.

The invention overcomes problems previously plaguing the art wherein hotrolling technologies did not permit P to be used at levels as instantlyclaimed. Also the instant invention provides an alloy that can containif desired, a wide range of Sn content, for example, greater than 7% Sn,(including 8-11% Sn in several embodiments) with excellent workingproperties and product characteristics. Although below 8% Sn content ispreferred for greater electrical conductivity desired in someapplications, higher-levels of Sn will provide greater strength desiredin other applications. In contrast, many applications will demand thatthe Sn content be 8% by weight or less, for example, 7%, 5%, andpossibly approaching 3%. For some applications, a 1% Sn content mayprove advantageous due to its high electrical conductivity and moderatestrength. Alloys with Sn content below 1% will have lower potentialstrength levels and will not achieve the contact forces required in somemore demanding spring contact applications.

P levels of 0.01-0.20 may prove particularly advantageous in manyapplications.

Ni and Si in the phosphor bronze according to the invention allowimproved strengths and will increase the alloy's resistance to stressrelaxation at elevated temperatures where the alloy may be used.

The instant invention provides a metal alloy comprising by weight:

Sn  1.0-11.0% Ni 0.4-3.0% Si 0.1-1.0% P 0.01-0.35%

Cu comprises the balance. Preferred embodiments of this invention may belimited to preferred subranges of various components, e.g., Sn contentof below 8%, 1.0 to 1.5%, 2.1 to 2.7%, 4.7-5.3%, 1-7%, 7-11%, 7-8% or7-9%, etc. Similarly, other constituents such as P may be preferablylimited to, for example, 0.01-0.2%, 0.01 to 0.06%, 0.05-0.18 or 0.2,etc, Si content can be 0.22-0.30% or 0.4-0.5%. Ni content can be1.3-1.7%, 2.5-3.0%, or 1.0-3.0%, etc.

Of course, the inventors contemplate that a small amount of impuritiesthat are not economically avoided will be present.

In other preferred embodiments of the invention, this alloy consistsessentially of, by weight:

Sn  1.0-11.0% Ni  0.4-3.0% Si  0.1-1.0% P 0.01-0.35%, or smallerpreferred ranges of each element, with the balance being Cu.

In a more preferred embodiment, the inventive alloy consists essentiallyof:

Sn  1.0-7.0% Ni  0.4-3.0% Si  0.1-1.0% P 0.01-0.2%, with the balancebeing Cu. Again, smaller specific subranges are contemplated asapplications dictate.

In yet other preferred embodiments of the invention, the alloy consistsof, by weight:

Sn  1.0-11.0% Ni  0.4-3.0% Si  0.1-1.0% P 0.01-0.35%, or especially, Sn 1.0-7.0% Ni  1.0-3.0% Si  0.2-1.0% P 0.02-0.2%, in each case with thebalance being Cu.

Based on preliminary analysis, the alloys according to the instantlyclaimed invention will demonstrate improved properties, for example,conductivity and tensile strength, over those alloys known in the art.Devices incorporating the alloy will be more economical to produce andmaintain and will demonstrate improved durability. Table 1 shows acomparison of exemplary alloys according to the invention, with severalstandard phosphor bronze alloys.

EXAMPLE

In one embodiment of the instant invention, an alloy designated alloyMHP101 was cast with the chemistry as follows:

Cu 95.67%, Sn 2.46%, P .057%, Ni 1.50%, Si 0.28% together withunavoidable impurities.

The material was processed to 0.0070″ thick and had mechanicalproperties as follows in the bare conditions unless otherwise stated:

Tensile strength 91.9 ksi Yield strength @.2 84.4 ksi Elongation on 2″13.9% Grain size .010 mm Conductivity 31.1% I.A.C.S. Good way bend (180deg) Flat at .690″ wide, bare Bad way bend (180 deg) Radius .006″ at.690″ wide, bare Flat at .690″ wide, tinned 40 microinches per side Badway bend (180 deg) Flat at .020″ wide, bare. Modulus of Elasticity 20psi × 10⁶, tension Density .323 lbs/cu inch at 68° F.

The softening behavior is shown in FIG. 1 compared with data of C51100alloy (4Sn Phosphor Bronze) and C52100 (8% Sn Phosphor Bronze). The timeat temperature was one hour.

The stress relaxation behavior is shown in FIG. 2 compared with C51100alloy. The test stress was 80% of initial stress, and the initial stressin the test sample was 88ksi. The test temperature was 150° C.

Expected electronic application guide data for MHP101 and other alloysaccording to the instant invention compared to similar UNS designatedalloys are shown in Table 1.

TABLE 1 ELECTRONIC APPLICATIONS ALLOY GUIDE Tensile Strength ChemistryConductivity (KSI)/n/mm² Alloy (Nominal %) (% IACS) Hard Spring *MHP 2Cu, 1.5 Sn, 1.5 Ni, 40 70/483 85/586 0.30 Si, 0.2 P max min** min *MHP 5Cu, 2.4 Sn, 0.5 Ni, 35 70/483 85/586 0.10 Si, 0.2 P max min min *MHP 105Cu, 5.0 Sn, 1.5 Ni, 13 82/565 100/690 0.3 Si, 0.2 P max C 51000 Cu, 5Sn, 0.2 P 15 76-91/ 95-110/ 524-628 655-759 *MHP 101 Cu, 2.4 Sn, 1.5 Ni,30 75/517 90/620 0.3 Si, 0.2 P max C 51100 Cu, 4.2 Sn, 0.2 P 20 72-87/91-105/ 496-600 628-724 C 51900 Cu, 6 Sn, 0.2 P 14 80-96/ 99-114/552-662 683-786 *MHP 108 Cu, 7.5 Sn, 1.5 Ni, 10 90/620 110/758 0.3 Si,0.2 P max C 52100 Cu, 8 Sn, 0.2 P 13 85-100/ 105-119/ 586-690 724-821*MHP 109 Cu, 7.5 Sn, 2.75  9 95/655 110/758 Ni, 0.45 Si, 0.2 P max *MHP100 Cu, 1.5 Ni, 1.25 40 70/483 85/586 Sn, 0.3 Si, 0.2 P max C 50500 Cu,1.3 Sn, 0.35 P 48 59/407 70/483 max *MHP 4 Cu, 7.5 Sn, 0.5 Ni, 12 85/586105/724 0.10 Si, 0.2 P max min min *New alloy composition and expectedproperties. **min = minimum “MHP” is a trademark of The Miller Company,the assignee of the invention of the subject patent application.

The data collected for MHP101 confirm that alloy formulations of theinstant invention provide resistance to stress relaxation at highertemperatures than the current offering to standard Phosphor Bronzealloys such as the C51100 used in the comparison. In addition, strengthsequal to higher tin-containing Phosphor Bronzes can be achieved withincreased electrical conductivity.

The alloy MHP101, an example of the alloys of the instant invention, isthus shown to have excellent formability properties.

It also has a higher modulus of elasticity which offers the connectordesigner a material with increased contact forces for a givendeflection.

The invention also provides the above described alloy for use as acasting material.

The invention also includes embodiments for certain applications thatmay demand smaller ranges of constituents, e.g., 0.02-0.2% P, thandescribed above. All subranges within the above-described ranges arecontemplated as part of the invention.

Sn over 7%, for example, nominal. Sn content of 8%, 9%, or 10% will addstrength to the alloy. The alloy will also have better formability at agiven tensile strength.

The invention especially includes embodiments where the alloy displaysproperties of solid solution hardening, and precipitation hardening, anddispersion hardening.

Another aspect of the invention is a phosphor bronze casting. Theproduct resulting from the processing of the casting is useful as amaterial for electrical lead conductor applications. Such applicationsinclude those relating to integrated circuits and those encountered inthe automotive industry such as engine compartment circuitry.

What is claimed is:
 1. An electronic connector or an electronic switchcomprising a phosphor bronze alloy consisting of 0.4 to 3.0 wt. % Ni,0.1 to 1.0 wt. % Si, 0.01 to 0.06 wt. % P, 1.0 to 11.0 wt. % Sn and theremainder being Cu.
 2. The electronic connector or electronic switch ofclaim 1 wherein the Ni content is 1.0 to 3.0 wt. %.
 3. The electronicconnector or electronic switch of claim 1 wherein the Sn content isbelow 8 wt. %.
 4. The electronic connector or electronic switch of claim1 wherein the Si content is 0.22-0.30 wt. %.
 5. The electronic connectoror electronic switch of claim 1 wherein the Si content is 0.4-0.5 wt. %.6. The electronic connector or electronic switch of claim 1 wherein theSn content is 1-7 wt. %.
 7. The electronic connector or electronicswitch of claim 1 wherein the Sn content is 1.0-1.5 wt. %.
 8. Theelectronic connector or electronic switch of claim 1 wherein the Sncontent is 2.1-2.7 wt. %.
 9. The electronic connector or electronicswitch of claim 1 wherein the Sn content is 4.7-5.3 wt. %.
 10. Theelectronic connector or electronic switch of claim 1 wherein the Sncontent is 7-11 wt. %.
 11. The electronic connector or electronic switchof claim 1 wherein the Sn content is 7-8 wt. %.
 12. The electronicconnector or electronic switch of claim 1 wherein the P content is0.05-0.06 wt. %.
 13. The electronic connector or electronic switch ofclaim 1 wherein the Ni content is 1.3-1.7 wt. %.
 14. The electronicconnector or electronic switch of claim 1 wherein the Ni content is2.5-3.0 wt. %.
 15. The electronic connector or electronic switch ofclaim 1 wherein the Ni content is 1.3-1.7 wt. %, the Si content is0.22-0.30 wt. %, the P content is 0.01-0.06 wt. %.
 16. The electronicconnector or electronic switch of claim 15 wherein the Sn content is1.0-1.5 wt. %.
 17. The electronic connector or electronic switch ofclaim 1 wherein the Ni content is 2.5-3.0 wt. %, the Si content is0.4-0.5 wt. %, the P content is 0.01-0.06 wt. % and the Sn content is7.0-8.0 wt. %.
 18. The electronic connector or electronic switch ofclaim 1 consisting of 1.5 wt. % Ni, 0.28 wt. % Si, 0.057 wt. % P, 2.46wt. % Sn and the remainder being Cu.
 19. The electronic connector orelectronic switch of claim 1 which is an electronic switch.
 20. Theelectronic connector or electronic switch of claim 1 wherein the Sncontent is 1.25 wt. % nominal to 11.0 wt. %.
 21. The electronicconnector or electronic switch of claim 15 wherein the Sn content is2.1-2.7 wt. %.
 22. The electronic connector or electronic switch ofclaim 15 wherein the Sn content is 4.7-5.3 wt. %.
 23. The electronicconnector or electronic switch of claim 15 wherein the Sn content is7.0-8.0 wt. %.
 24. The electronic connector or electronic switch ofclaim 1 which is an electronic connector.
 25. A phosphor bronze castingcomprising a phosphor bronze alloy consisting of 0.4 to 3.0 wt. % Ni,0.1 to 1.0 wt. % Si, 0.01 to 0.06 wt. % P, 1.0 to 11.0 wt. % Sn and theremainder being Cu.